Catalytic cracking of heavy hydrocarbons in two stages



muy 10, 1951 G. l. JENKINS CATALYTIC CRACKING oF HEAVY HYDRocARoNs 1NTwo STAGES Filed July 29, 1948 XUDN WQWWIK MM ws. n.

IM W ,w m h ,W

atentecl 1Y0, 1,951

CATALYTC CRACKING OF HEAVY HYDRO- CATtBONS IN TWO STAGES Gwilym IslwynJenkins, Sunbury-onJihames,

England, assigner to Anglo-Iranian Oil Company Limited, London stockcorporationl England, a British joint- @pplication July 29, 1948, SerialNo. 41,268 In Great Britain August 9, 1947 The invention relates to thecatalytic crack- 6 Claims. (Cl. 196--49) ing of heavy hydrocarbons, suchas wax disn tillates. l

The reaction products obtained by the catalytic cracking of heavyhydrocarbons, such as Wax distillate, may conveniently be divided intothree fractions, viz. gaseous hydrocarbons, cracked motor gasoline andcracked gas oil, all three fractions boiling belowthe boiling range ofthe feedstock. We Ahave found that the conditions under which thecracking reaction is carried out may be varied to obtain on the one handa cracked motor gasoline having a high octane number,'and of commercialvalue, without re-treating or blending, in which case the cracked gasoil is of poor quality and is of doubtful value, particularly as aDiesel fuel, or on the other handl a gas oil of much better quality, anda -lower yield ofv motor gasoline of lower Octane number. Thus, forexample, if a high severity cracking process resulting in approximately75 to 80% feedstock destruction is employed, there is a yield of 33%gasolineof 81 octane number and a yield of 18% gas oil having a Dieselindex of only 7. Such a gas oil can only be utilised as a blending stockfor thel improvement of the pour-point of a fuel oil. Ifa low severitycracking process be employed, forA example, a process `'carried outunder conditions of high feed ratev and relatively low catalystcirculation rate such that the feedstock destruction amounts to 40 to xby 3% and Vfurthermore such small decrease is more than compensated forby the increased feed-rate permissible at the lower .feed-stock delstruction; The low ,severity cracking process suffers from thedisadvantage, however, that there is alarge residue amounting to 55% to60% of the feedstock and having substantially the same boiling rangeasgthe. feedstock. y

lThe inventionI has ,amongl its objects' to .pro-

vide a process which embodies the advantages of f both the high severityvandjow'severity cracking Lprocesses so as to obtain the maximum yieldsof gasoline, gas oil vand fuel oil having the optimum octane number,

u Diesel index and pourpointy respectively.

According to; theinv'entionthvere is provided a two-stage process forthe catalytic cracking ofA y a heavy hydro'carbon'vf'eedstock, suchyfalsgigzai; dis-f tillate, in which in the rst stage the feedstock iscracked under conditions resulting in rela-' tively low feedstockdestruction to give a high yield of gas oil suitable for use as a Dieselfuel, while in the second stage the residue from the first stage iscracked under conditions resulting in relatively high feedstockdestruction to give a high yield of good quality motor gasoline and aresidue constituting a source of fuel oil having `a low pour-point dueto the presencevin the residue of cracked gas oil.

The process of the invention may be carried into effect in various Waysaccording to refinery as overhead through line I4, and a gas oil havxing a high Diesel index as side stream through line I5. A residueboiling above the gas oil range is 'separated as bottoms through linei6. The overhead product is passed to a second fractionator Il where thegas is separated overhead ,through line I8 and the stabilised gasolineas a bottoms product through line I9, the residue' from fractionator I3being passed to a second reactor 2li where it is cracked under highseverity conditions resulting in the production of a gasoline of highoctane number. The re.-

`action products from the second reactor are' passed through line 2i toa third fractionator 22 Where the gasoline and lighter hydrocarbons areseparated as overhead through line 23 and a bottoms product withdrawnthrough line 24 consisting of residual material containing cracked gasoil produced in the second reactor.

The overhead products from the third fractionator 22 may be passedthrough line 25 to the second fractionator Il in conjunction with theoverhead products from the first fractionator, so that the gasolineproduced in the first reactor is improved in octane number by theaddition of the gasoline of higher octane number produced in the secondreactor. If desired, however, the

overhead product from the third fractionatol` 22 i may be passed throughline 2li to a separate stabiliser 2l so as to provide a gasoline of highoctane number as compared with the gasoline of low octane numberseparated from the second' fractionator, the gasoline ibeing removed asa bottoms product through line 28 and the gas overhead through line 29.

The two-stage process of the invention may be carried into effectaccording to any of the Wellknown operating principles. Thus, forexample, both loivrconversion and high-conversion operations may becarried out in reactors, both of -which are operated on the normaldownow or bottom catalyst draw-off, uidised bed principle.Alternatively, it is particularly satisfactory to use a first reactoroperating on the well-known uplow fluidised principle, in order to dealconveniently with the high linear velocities often necessary for lowconversion, while the second reactor is operated on the normal downflowprinciple. Where both reactors are of the uidised or moving bed type, itis possible to utilise either a single regenerator serving bothreactors, or a separate regenerator for each reactor.

The improvement obtained by means of the process according to theinvention is clearly brought out in the following tables.

' Table I gives the experimental results obtained when processing a waxdistillate of Iranian origin on a synthetic silica-alumina catalystunder conditions of high and of low cracking severity. The reactortemperature, pressure and dilution were identical in both cases, but theoil throughput, expressed as weight of oil per hour per unit of weightof catalyst in the reactor Wo/H/Wc, was more than twelve times as greatin the low severity operation as in the high severity operation. Inorder to provide direct assessments of the two modes of operation theexperimental data provided in Table I have been transferred tocomparative bases and the results are given in Tables II and III. InTable II the high and low severity operations are compared on the basisof equal oil feed rate, a value of 10,000 barrels per stream day beingchosen as the basis for comparison. In Table III the two operations arecompared on the basis of equal quantities of catalyst i. e.approximately equal reactor dimensions. Table IV gives the results ofoperating the two-stage piocess according to the invention, while TableV gives a comparison between the two-stage process and the normal singlestage process.

In the following tables andk throughout this speciiication the feedstockconversion is dened as 100 minus the volume percentage of material, inthey reaction product, boiling above a true boiling point temperature of430 F.

Table I Feedstockfwax distillate of Iranian origin. Catalyst-syntheticsilica-alumina.

High Low Severity Severity Reactor Conditions:

Temperature'.... F.. 900 900 Outlet Pressure. ...p. s. i. g-. 10.0 10.Space. Velocity Wo/H/Wc.- 0.81 10.3 Dilution (as steam) weight per centon feed.. l2. 7 13.1 Product Yields:

Ca and lighter....weiglit per cent oii feed.. 8. 26 2. 31 Total O4-.do.... 10.3 1.98 Debutginised Gasoline ..do.-.. 33.1 17. 2 GasOil..do.... 18. 2 14.6 Residue -do.- 24.1 60.3 Coke hydrogen) `.do.... 5.0Feedstock Conversion: 1130" Basis Volume per cent.. 60.0 24. 5 ProductProperties:

Gasoline End-point C.. 208 209 Gasoline O. N 81 76. 5 Sulphur .weightper cent.- 0.09 0.19 Gas Oil Diesel Index.- 7 20 Gas Oil Pour Point.-.F.. -5 +5 Gas Oil Sulphur weight per cent.. 2. 26 2.14

Table JI Feedstock and catalyst-as in Table I.

60% 25.5% Couver- Conversion sion Oil Feed-rate .B. P. S. D-. 10,00010,000 Catalyst in reactor lbS.. 163, 700 12, 870

Products C3 and lighter.. .SCF/bbl.. 251 75 T al Cl .B. S. D.. 1,630 316Gasoline (400 F. E. P.):

' 77 O. S. D 2, 040 (b) 81 O. N B. P. S. D-- 4,090 Gas Oil (0 F. Pour):

` (a) 20 D.v IL .B. P. S. D 1, 450 (b) 7 D. I.... S. D.. 1,730 Residueabove Gas oil.. Y S. D.. 2,330 6,080

Table III Feedstock and catalyst-as in Table I.

@ 60% 24.5% Oonver- Conversion sion Oil Feed-rate. 10,000 Catalyst inrea l 12,870

C3 and lighter. 75 T al C S. 316 Gasoline (400 (l) 77 2.040 (2) 8i GasOil (0 (l) 20 1,450 (2) 7 D. iso Residue above G 183 6, 080

Tabl@ IV Catalyst and feedstock-as in Table I.

Process A-reactor operating at low conversion (24.5%) with fresh'feed'.

Process -reactor operating at high conversion on residue from processA..

Process A+B"-net result ou operating A and 13" in series withsegregation of gasolines and gas oils.

Process .A'fnet result on operating A" and YB in series with combinationof gasoline's and gas oilsvirito single streams.

Process Ref.

A+B AB Oil Feed Rate-Fresh B. P. s. D-- io, 000 Nili 10,000 Oil FeedRate-Residue B. P. S. D.. Nil Catalyst iny Reactor(s) .-...1bs.. 12, 870Feed'stock Conversion LevelY i Basie igesh reed.

Table V Catalyst and feedstock-as in Table I. Process S"si11gle reactoroperating at 60% conversion level. Process A+B-dual system withsegregation of gasolines and Process Ref.

S A+B AB Oil Feed Rate-Fresh- B. P. S. D-- 10,000 10,000 10,000 Catalyst111 total system lbs.- 163, 700 111, 600 111, G00

Products O3 and lighter sGF/BbLL- 251 22s 228 Total C4 B. P. S. D..1,630 1, 310 1,310 Gasoline (400 77 O B. S. D. 2,040

(b) 81 O. N B. P S. D-- 4,090 4, 530

(c) 79 O. N B. P S. D.. 4,530 Gas Oil (0 F. Pour):

(il) 20 D. I B. P. S. D-- 1,450

c approx Residue 2, 330 1, 420 l, 420

1 Basic fresh feed.

It will be seen from a consideration of Table II that although thereaction space required for processing 10,000 B. P. S. D. at aconversion of 24.5% is less than one-tenth of that required for the samequantity of feed at 60% conversion, the gas oil yield is only 280 B. P.S. D. less at the lower conversion while the Diesel index is 13 unitshigher. It will be seen from a consideration of Table III that the lowconversion operation yields 1450 B. P. S. D. of gas oil of 20 Dieselindex as compared with only 136 B. P. S. D. of 7 Diesel index in thehigh conversion operation.

It is also clear from Tables IV and V that the two-stage process isadvantageous as compared with the single stage process in many respectsand particularly with regard to gas oil yield and quality. Thus, thetota1 catalyst requirement in the two-stage process is 52,000 lbs. lessthan in the single stage process. The single stage process gives moregas and volatiles, thus requiring a larger gas-handling plant, and some900 B. P. S. D. more cracked residue. The total quantity of gas oil inthe two-stage process, is 2,500 B. P. S. D. of which 1450 B. P. S. D. isat 20 Diesel index and the remainder is at 7 Diesel index. The Dieselindex of the combined material is estimated as being 15. With the singlestage process, the gas oil yield is only 1730 B. P. S. D. and the Dieselindex is 7. The single stage process gives 4090 B. P. S. D. of gasolineof 81 octane number, while by combining the two gasolines from thetwo-stage process there is a total yield of 4530 B. P. S. D. at anestimated octane number of 79, or, on an alternative basis, thetwo-stage process yields 358,000 barrel-octane numbers as compared with331,000 BON from the single stage process.

I claim:

1. A two-stage process for the catalytic cracking of a hydrocarbonfeedstock boiling above the gas oil range, comprising passing thefeedstock to a reactor wherein it is cracked at a relatively high spacevelocity resulting in approximately iO-45% feedstock destruction,passing the reaction products from the reactor to a fractionator s. 6Where gasoline having an octane number about 77 and lower hydrocarbonsare separated as overhead, a gas oil having a Diesel index ofapproximately 20 as a side stream and a residue boiling above the gasoil range as bottoms, removing the gas oil from the system, passing theoverhead product to a second fractionator where the gas is separatedoverhead and the stabilized gasoline as a bottoms product, passing theresidue boiling above the gas oil range to a second reactor where it iscracked at a relatively low space velocity resulting in approximately 75-80% feedstock destruction, and passing the reaction products from thesecond reactor to a third fractionator where gasoline having an octanenumber about 81 and lighter hydrocarbons are separated as overhead, anda bottoms product is withdrawn consisting of residual materialcontaining cracked gas oil having a Diesel. index about 7 produced inthe second reactor and constituting a source of fuel oil.

2. A two-stage process according to claim 1, in which the overheadproducts from the third fractionator are passed to the secondfractionator in conjunction With the overhead products from the firstfractionator and gasoline is separated from the second fractionator, theyield of gasoline so produced having a greater total barrel octanenumber than the yield of gasoline which could be obtained by crackingthe original feedstock in a single stage.

3. A process according to claim 1, in which the overhead product fromthe third fractionator is passed to a separate stabilizer where the gasis separated overhead and the gasoline of octane number approximately 81is separated as a bottoms product.

4. A process according to claim 1, wherein the first reactor operates onthe up-ow fluidized principle, while the second reactor is operated onthe down-flow principle.

5. A process according to claim 1, wherein cracking in the first reactoris carried out at a temperature of 900 F., a pressure at the outlet ofthe reactor of 10 lbs/sq. in., and a space velocity of 10.3 Wo/H/Wc.

6. A process according to claim 1, wherein the cracking in the secondreactor is carried out at a temperature of 900 F.; a pressure at theoutlet of the reactor of 10 lbs/sq. in., and a space velocity of 0.81Wo/H/Wc.

GW ILYM ISLWYN JENKINS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,271,670 Thomas Feb. 3, 19422,326,705 Thiele et al Aug. 10, 1943 2,339,874 Nysewander Jan. 25, 19442,353,731 Kanhofer July 18, 1944 2,444,131 Seguy June 29, 1948 2,444,545Thomas July 6, 1948 OTHER REFERENCES Production of Premium Diesel Fuels,George M. Woods, part 2, The Petroleum Engineer. Dec. 1936, pages 58,60, 62, 64.

Certificate of Correction Patent No. 2,560,511 u July 10, 1951 GWILYMISLWYN JENKINS It is hereby certified that error appears inthe printedspecification of the above numbered patent requiring correction asfollows:

Column 4, Table II, in the heading to the third column thereof, for25.5% read 24.5%

and that the said Letters Patent should be read as corrected above, sothat the same may conform to the record of the case in the PatentOiiice. Signed and sealed this 25th day of September, A. D. 1951.

[SEAL] THOMAS F. MURPHY,

Assistant Commissioner of Patents.

1. A TWO-STAGE PROCESS FOR THE CATALYTIC CRACKING OF A HYDROCARBONFEEDSTOCK BOILING ABOVE THE GAS OIL RANGE, COMPRISING PASSING THEFEEDSTOCK TO A REACTOR WHEREIN IT IS CRACKED AT A RELATIVELY HIGH SPACEVELOCITY RESULTING IN APPROXIMATELY 40-45% FEEDSTOCK DESTRUCTION,PASSING THE REACTION PRODUCTS FROM THE REACTOR TO A FRACTIONATOR WHEREGASOLINE HAVING AN OCTANE NUMBER ABOUT 77 AND LOWER HYDROCARBONS ARESEPARATED AS OVERHEAD, A GAS OIL HAVING DIESEL INDEX OF APPROXIMATELY 20AS A SIDE STREAM AND A RESIDUE BOILING ABOVE THE GAS OIL RANGE ASBOTTOMS, REMOVING THE GAS OIL FROM THE SYSTEM, PASSING THE OVERHEADPRODUCT TO A SECOND FRACTIONATOR WHERE THE GAS IS SEPARATED OVERHEAD ANDTHE STABILIZED GASOLINE AS A BOTTOMS PRODUCT, PASSING THE RESIDUEBOILING ABOVE THE GAS OIL RANGE TO A SEOND REACTOR WHERE IT IS CRACKEDAT A RELATIVELY LOW SPACE VELOCITY RESULTING IN APPROXIMATELY 75-80%FEED-